A biometric and taxonomic study of Miocene-age, hydrocarbon-seep mussels from the East Coast of the North Island, New Zealand

Abstract

Subduction-related, Miocene-age, cold hydrocarbon seep deposits occur along 300 km of the East Coast Basin, North Island, New Zealand. These carbonates contain seep-restricted paleocommunities which are typically dominated by large numbers of fossil mussels associated with methane rich fluid expulsion. These fossil mussels are found in 10 of 13 Otaian to Tongaporutuan seep carbonate sites where numerous blocks were collected. A biometric analysis of shell linear measurement ratios revealed three populations of mussels, each with distinct morphologic characteristics. Further statistical analyses compared these three identified groups of fossil mussels with seven species of living hydrothennal vent and cold hydrocarbon seep mussels that belong to the genus Bathymodiolus, Kenk and Wilson (1985). The results of this comparison showed that one of the fossil populations (Group 2) shared many shell characteristics with Bathymodiolus aduloides,. Hashimoto and Okutani, 1994, from hydrothermal vents and cold seep sites near Japan. The remaining two fossil populations (Groups 1 and 3) did not show many morphologic similarities with the living species.